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Let’s suppose we wanted to write a new GNU make function that
would create a temporary file and return its name. We would like our
function to take a prefix as an argument. First we can write the
function in a file mk_temp.c:
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <gnumake.h>
int plugin_is_GPL_compatible;
char *
gen_tmpfile(const char *nm, int argc, char **argv)
{
int fd;
/* Compute the size of the filename and allocate space for it. */
int len = strlen (argv[0]) + 6 + 1;
char *buf = gmk_alloc (len);
strcpy (buf, argv[0]);
strcat (buf, "XXXXXX");
fd = mkstemp(buf);
if (fd >= 0)
{
/* Don't leak the file descriptor. */
close (fd);
return buf;
}
/* Failure. */
fprintf (stderr, "mkstemp(%s) failed: %s\n", buf, strerror (errno));
gmk_free (buf);
return NULL;
}
int
mk_temp_gmk_setup (const gmk_floc *floc)
{
printf ("mk_temp plugin loaded from %s:%lu\n", floc->filenm, floc->lineno);
/* Register the function with make name "mk-temp". */
gmk_add_function ("mk-temp", gen_tmpfile, 1, 1, 1);
return 1;
}
Next, we will write a Makefile that can build this shared object, load it, and use it:
all: @echo Temporary file: $(mk-temp tmpfile.) load mk_temp.so mk_temp.so: mk_temp.c $(CC) -shared -fPIC -o $@ $<
On MS-Windows, due to peculiarities of how shared objects are
produced, the compiler needs to scan the import library produced
when building make, typically called
libgnumake-version.dll.a, where version is the
version of the load object API. So the recipe to produce a shared
object will look on Windows like this (assuming the API version is 1):
mk_temp.dll: mk_temp.c $(CC) -shared -o $@ $< -lgnumake-1
Now when you run make you’ll see something like:
$ make mk_temp plugin loaded from Makefile:4 cc -shared -fPIC -o mk_temp.so mk_temp.c Temporary filename: tmpfile.A7JEwd
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